1. Field of the Invention
The invention relates to backlight modules, more particularly to a backlight module using replaceable external electrode lamps.
2. Description of the Prior Art
Most TFT-LCD (thin film transistor liquid crystal display) displays today utilize cold cathode fluorescent lamps (CCFL) for their backlight modules, where the electrodes of the lamps are effectively sealed inside. The electrode contains a conducting end that extends from the internal electrode to an external conducting wire. The conducting wire then connects to a power supply in order to draw energy for the lamp.
The conducting end of the CCFL is typically connected to the conducting wire through either a welding or a copper belting process. The welding or copper belting processes however, are both rather complicated and may result in high failure rates during operation. For example, poor soldering can often cause a fake welding effect. Fake welding effects are particularly susceptible to melting or breakage upon the lighting of the electrode, as sufficient heat is generated that will result in temperatures high enough to melt solder and damage the area of the fake weld. Also, if excess solder is located between the conducting end and the conducting wire, an electric discharge can result that can cause scorching or electrical leakage. When using a copper belting process, considerations for the potential electric discharges at the four corners of the copper belt must be made. This problem is typically addressed through the addition of an insulated heat-shrink tube to cover the external area of the copper belt, resulting in additional manufacturing costs for the CCFL.
Taiwan Patent No. 00540745 provides a backlight device that includes a set of lamps located inside a main structure, in which each of the lamps contains a conducting end extending from the internal lamp. The main structure includes a plurality of supporting devices, in which each of the devices contains a hole capable of holding a lamp, and a conducting element that electro-mechanically connects to the conducting end of the lamp. Although this patent design essentially manages to solve the aforementioned problems, the luminosity and life expectancy of the lamp proves more and more inefficient as backlight lamp technologies advance, and LCD panel sizes continue to increase. In order to cope with these increasing challenges, an external electrode fluorescent lamp (EEFL) was introduced.
EEFLs are a type of illumination device for transforming electrical energy into light energy released at high frequencies. In contrast to other fluorescent lamps that use an electrode to transform electrical energy into light energy, EEFL utilizes electromagnetic induction through a pair of metal electrodes covering the lamp to generate an internally induced current. A pair of metal electrodes covering the lamp is used as a primary coil of an adapter, whereas the lamp is being used as a secondary coil of an adapter.
Using the same amount of current, the luminosity of an external electrode fluorescent lamp is noticeably higher than that of a cold cathode fluorescent lamp. Moreover, the life expectancy of external electrode fluorescent lamp is significantly longer than that of cold cathode fluorescent lamps, as CCFLs usually last around 60,000 hours, whereas EEFLs last between 80,000 to 100,000 hours. As a result, external electrode fluorescent lamps have been gradually integrated into TFT-LCD backlight modules due to the significant advantages they offer.
Although EEFLs exhibit several benefits over CCFLs, they are not without their disadvantages. Because the electrodes of EEFLs are constantly driven by high voltages while being exposed to external environments, numerous electric shocks are commonly experienced. In addition, the layout of the electrode power supply used to stabilize the external electrode lamp places various limitations on the shock resistance design. Consequently, many of the EEFL products sold in the market today still suffer from problems such as poor electrode cladding and poor shock resistance.
Conventional LCD backlight modules using EEFL have the lamps electrically connected in parallel on a back plate, with the backlight module attached to the optical film of the LCD panel. If any single lamp becomes damaged or broken, the overall illumination decreases, resulting in a poor display quality. To restore the illumination levels to back to factory specifications, the damaged or broken lamps should be replaced. This is accomplished by first disassembling the LCD, removing the lamp holder, replacing the damaged or broken lamp, and finally reassembling the removed components. The replacement of damaged lamps is therefore a tedious and precise process that introduces the possibility of damaging other components during repair. In particular, other components such as adjacent lamps, optical film sets, and the driver circuit are very fragile, and are easily susceptible to damage when replacing a damaged lamp. As LCDs become larger and larger, the effort required to replace lamps in an LCD becomes increasingly larger and more difficult.
Therefore, a need exists for a backlight module that allows for the simple replacement of backlight lamps, while minimizing the problems associated with EEFLs such as poor electrode cladding and poor shock resistance.